Question: Can you run OS X 10.10 on MacBook Pro 2018?
It would probably sounds strange to you, but as electronic musician I find OSX 10.10 quite lightweight and reliable. At the moment I use a 2015 MBP, it actually is my second one as the first got stolen. When the new one arrived it had macOS Sierra (which also runs on my girlfriend's mac) installed and I quickly realised it was a completely different environment (and much more buggy too), so I reinstalled OSX 10.10 from my time machine backup. By the way, this means that it's not true that you can't install an OS older than the one your mac shipped with.
Therefore, you think there's any chance to install OSX 10.10 on a newer, say 2018 MBP?
MacBook Pro with Retina display, OS X Yosemite (10.10.4)